1. Field of the Invention
The invention relates to an image processing apparatus and a processing method for improving a picture quality by properly setting an interpolating position when an image size is converted by using a linear interpolation.
2. Description of the Related Art
Hitherto, for example, in a television receiver, it is demanded to display simultaneously or one to plural slave picture planes reduced at, for example, an arbitrary ratio for a main master picture plane. In such a case, hitherto, when a pixel number conversion for reduction display is performed, an interpolation origin is fixed and an interpolating process is executed at a pixel position obtained at an interval according to a conversion ratio.
A method called a linear interpolation is known as an interpolation processing method when enlarging or reducing at an arbitrary ratio while preventing a deterioration of a picture quality. According to the linear interpolation, a position on an original image of an arbitrary pixel in a conversion image obtained by enlarging or reducing the original image is obtained and a dense/thin value of the above point in the conversion image is obtained on the basis of dense/thin values of pixels at four points near the obtained position in the original image.
In such an interpolating process, however, a portion where the pixel position of the original signal and the pixel position after the interpolation coincide periodically occurs in dependence on a conversion ratio. In this case, the pixel of the same dense/thin value as that of the original image and the interpolated pixel are periodically displayed. In the pixel having the same dense/thin value as that of the original signal and the interpolated pixel, since energies of the pixels are different, such a state is observed as glitter of the image, luminance variation, pixel missing, or the like on the picture plane, so that there is a problem such that the image is very hard to see. This problem exerts a large influence on, particularly, a character display.
To prevent it, hitherto, for example, a method of performing a pre-filtering process by a low pass filter before the interpolating process has been used. However, in case of enlarging or reducing the image at an arbitrary magnification, since the characteristics of the filter have to be adaptively changed, there is a problem that the optimum filtering process is difficult. There is also a case where the image contrarily becomes oblique depending on the process.